Man-made vitreous fiber wool

ABSTRACT

The production and physiological dissolution rate of mineral wool formed of MMV fibers containing 35-66% SiO 2 , up to 10% A1 2  O 3 , 10-45% CaO, 2-30% MgO, up to 10% FeO, 0-7% Na 2  O+K 2  O and 0-10% TiO 2  is improved by including both P 2  O 5  and B 2  O 3  in the composition.

This is a continuation-in-part of U.S. patent application Ser. No.08/525,590, filed Sep. 8, 1995, now U.S. Pat. No. 5,614,452.

BACKGROUND OF THE INVENTION

The present invention relates to man-made vitreous fibre (MMVF) woolcontaining iron and a relatively high amount of alkaline earth metals,and a low amount of alkali metals, conventionally known as stone, slagor basalt wool.

Various types of MMV fibres are known.

It is known, in the manufacture of traditional glass fibres, to includein the glass melt components which provide boron oxide (borate). Thiscan improve the glass and the glass melt. However, borate-containing rawmaterials are expensive and are normally not added at all if possible,especially when the product contains iron and has low alkali and highalkaline earth content, as in conventional rock, stone and slag melts.

Glass wool products usually have a relatively high content of alkalimetal (often above 13% Na₂ O+K₂ O). In this specification all analysesare expressed by weight of total composition measured as oxides. Glassfilament and glass wool are usually free of iron but often also containboron. Typically they contain less than 7% Al₂ O₃. However E-Glass is afilamentary or other non-wool product and can have high aluminium andlow or zero alkali metal. For instance JP-A-50090719 describes anE-Glass containing 15-16% Al₂ O₃, 9.5-10.5% B₂ O₃ and 5% P₂ O₃. It isfree of iron and sodium.

Glass fibres are described in EP-A-9418 which can have a wide range ofoptional components including, inter alia, iron, boron and phosphorous.None of the exemplified compositions contain both boron and phosphorousand they all have above 13% alkali metal oxide.

WO93/07741 describes fibres containing 0 to 4% P₂ O₅, above 13% Na₂ O,and up to 8% Al₂ O₃ for use in horticulture. B₂ O₃ can be present butthe total amount of impurities (including any B₂ O₃ which is included)must be not above 1%.

Glass wool is described in EP-A-412878 which has high alkali metalcontent (above 13%) and which contains borate. It is free of iron.Phosphorous is an optional component. It is included allegedly toimprove solubility of the fibres.

We are concerned with improving the solubility of the fibres in thosewools generally referred to as rock, stone, slag or basalt wools andwhich typically contain iron, a low amount of aluminium (below 10%), alow amount of alkali metal (below 7%) and a significant amount ofalkaline earth metal (above 12%).

It has been proposed that it would be desirable to provide such wools inwhich the MMV fibres are soluble in a physiological medium, inparticular lung fluid.

It is known that the composition of a fibre can significantly affect itssolubility. For instance, it is illustrated in WO87/05007 that fibreshaving a low alumina content, in particular alumina below 10% by weightof composition, have improved solubility in a physiological environment.It is also known that inclusion of phosphorus can improve solubility inthe physiological medium. This has been illustrated in the case of stonewool fibres in for instance EP-A-459,897. This discloses stone woolfibres which comprise 1 to 10% of phosphorus as P₂ O₃. This component issaid to provide solubility in the physiological medium. It can beassumed that increasing the amount of phosphorous within this rangeincreases solubility.

During the manufacture of MMVF wool the components which are to form thefibres are melted in a furnace, such as an electric, shaft, tank orcupola furnace. This produces a melt which may then be fiberised. Themelt usually has a melting point of around 1,400° to 1,600° C. and isthus heated to above this temperature in the furnace. It has been foundthat the inclusion of significant amounts of phosphorous in the melt canlead to some problems. For instance phosphorus may volatilise in thefurnace, leading to difficulties of controlling the composition. Inparticular increasing the amount of phosphorus can adversely influencemelt viscosity and properties. It increases the risk of the melt (whichcontains iron and little or no alkali metal and low aluminium)undergoing phase separation and crystallisation. This leads to theformation and accumulation of solid or slag material in or on theapparatus being used for forming the melt and converting the melt tofibres, and can cause increased amount of shot formation during thefibre-formation process, reduced material efficiency and higher costs.

It would therefore be desirable to form MMVF wool having solubilitycharacteristics of the type which would be expected in such wool fromthe use of relatively high phosphorus content while avoiding themanufacturing problems associated with relatively high phosphorouscontents.

These problems tend to increase as the content of phosphate in the meltincreases. For instance difficulties may arise as the content ofphosphate increases beyond 5%. It may be possible with some furnaces touse up to 10% phosphate but in general for processing purposes it isundesirable to include more than this.

However, even at low levels of alumina, and in particular when it is notpossible to provide a melt having very low levels of alumina,dissolution rates of the fibres are not as high as may be desirable atthese levels of phosphate.

Therefore it would be desirable to improve the solubility of MMV fibresin the physiological medium without the necessity for using amounts ofphosphate which lead to processing problems.

Fibres containing phosphorus and boron are mentioned in WO94/23801, fromwhich this application claims priority.

SUMMARY OF THE INVENTION AND BRIEF DESCRIPTION OF THE PREFERREDEMBODIMENTS

According to the invention there is provided MMVF wool formed of fibresformed from a composition comprising, by weight of oxides (with ironexpressed as FeO):

SiO₂ 35-66%

Al₂ O₃ up to 10%

CaO 10-45%

MgO 2-30%

FeO up to 10%

Na₂ O+K₂ O 0-7%

TiO₂ 0-10%

P₂ O₅ +B₂ O₃ and other elements--up to 20% and which includes both P₂ O₅and B₂ O₃.

We find surprisingly that the use of a phosphate- and borate-containingmelt can give fibres with adequate physiological solubility producedfrom a melt which has a combination of good processing, viscosity andtemperature characteristics, especially when the amount of Al₂ O₃ islow.

We find that an upper limit of 10% on the amount of phosphate assists inreducing manufacturing problems, especially phase separation. The amountis preferably 6% or less and is usually below 5%. We find that inclusionof borate increases the physiological solubility of the fibres withoutthe necessity for using larger amounts of phosphate, and allows the useof phosphate even in amounts below 5% whilst retaining adequatephysiological solubility. We also find that borate has the additionaladvantage that it improves the physical properties of the melt, inparticular it assists in reducing the melting point of the melt so thatthe risk of phase separation is reduced.

We also find that the use of boron in phosphorus-containing fibresresults in improved fibre properties. For instance tensile strength,modulus of elasticity and length to diameter ratio can be improved.Tensile strength can be >700 MPa. Fibre Modulus of Elasticity can be<150 GPa. Length to fibre ratio can be >700, especially when the fibresare made by a cascade spinner.

The melt viscosity of the composition at 1400° C. is preferably 10-70poise, preferably 15 to 30 poise.

The fibres preferably have a dissolution rate at pH 7.5 of at least 30nm/day, and preferably at least 50 or at least 60 nm/day, when measuredby the stationary set up method described in Environmental HealthPerspectives, Vol. 102, Supplement 5, October 1994, pages 83-86.

The wool of the invention may be provided in any known way. According tothe invention we also provide a process of production of MMVF woolformed of fibres having a composition as defined above, the processcomprising

providing raw materials to give the composition,

providing a furnace,

placing the raw materials in the furnace and heating them to atemperature between 1,400° C. and 1,600° C. to produce a melt,

fiberising the melt, and

collecting the fibres as a wool.

In this process we find all the advantages in processing characteristicsdiscussed above. Preferably the wool of the invention are made by thisprocess of the invention.

In the process of the invention the raw materials used to produce themelt may be any known raw materials which give the constituents of thecomposition. For instance, raw materials which may be used includediabase, cement, clay, olivine sand, silica sand, waste foundry sand,rasorite, colemanite and other boron-containing materials, converterslag, blast-furnace slag, electric arc furnace slag, iron oxide, wastestone wool, waste asbestos, lime, soda, glass waste, dolomite, bauxite,iron silicate, kaoline, calcium phosphate, quartz sand and other knownmelt ingredients.

The melt composition and hence the composition of the produced fibrespreferably comprises at least 45%, often at least 47 or 48%, SiO₂. Themount is usually below 64 or 65%, preferably below 60%. Often the amountof SiO₂ is from 53.5 to 64%.

The composition preferably has a low alumina content, generally below 6%and preferably below 4%. In general it is very expensive to provide rawmaterials which contain no alumina at all, so Al₂ O₃ is present to someextent, usually in amounts of at least 0.5%, although alumina amountsare generally kept as low as possible, preferably below 3 or 2%. Amountsof 1-4% are often suitable.

The composition usually comprises at least 5%, generally at least 10%and preferably at least 15% alkaline earth metal oxides (CaO and MgO).Generally the amount is not more than 50%. Preferably CaO is containedin amounts of between 10 and 35%. In some compositions amounts of 10-20%are preferred but in others amounts of 15 to 30% are preferred. MgO isusually present in an amount of at least 1%, often 5 to 20%, preferably7 to 20%. For instance it may be in the range 5-15%.

The composition contains iron, and the amount is up to 10% by weight oftotal composition, measured as FeO. Preferably iron is present inamounts of at least 0.5 or 1%. Amounts of up to 4% are often suitablebut amounts may be up to 9 or 10%, e.g., in the range 6.5-9%.

The composition may comprise alkali metals (Na₂ O and K₂ O) in amountsof 0% up to 6% or 7%. In general Na₂ O is present in amounts of 0% up to4% and K₂ O is present in amounts up to 2%. Usually each is present inan amount of at least 0.1%, but both are optional and can be omitted.

Phosphate is present in the composition, generally in amounts of between0.5 and 10%, measured as P₂ O₅, and often in the range 3 to 6%. Forprocessing purposes it is desirable to keep the amount of phosphate aslow as possible whilst incorporating enough to give an adequatedissolution effect. Preferably the phosphate amount is at least 0.5 butbelow 5% (e.g., up to 4.5%), more preferably below 4%. Usually it is atleast 2% or 3%.

Borate is incorporated in useful amounts of up to 10%, measured as B₂P₃. The amount is preferably above 0.5 or 1%. In general, enough shouldbe added to increase suitably the physiological dissolution rate, butincorporation of large amounts of borate necessitates the use of veryexpensive raw materials. Amounts of borate below 5% (e.g., 4.5 andbelow) can give good results at economic cost but amounts up to 7 or 8%are sometimes preferred. The amount must be sufficient to give a usefuleffect and so is normally above 0.5 or 1% and preferably it is at least3%. The amount of B₂ O₃ is usually below the amount of P₂ O₅ for reasonsof economy.

TiO₂ is optional. If present, its amount is usually 0.1 to 2%. The meltcomposition may additionally comprise 0 to 20% of other ingredients, forinstance BaO, ZnO, ZrO₂, F₂, MnO, Li₂ O, SrO. The total amount of otheringredients is usually not more than 5%, or at most 10%.

The composition of the melt and of the fibres particularly preferablycomprises:

SiO₂ 45-64%, preferably 47-60 or 48-60%

Al₂ O₃ 0.5 to 4%

CaO 10-35%,

MgO 5-20%, preferably 5-15 or 7-15%

FeO 1-10%, preferably 1 to 9%

Na₂ O 0 to 4%

K₂ O 0 to 2%

TiO₂ 0 to 2%

P₂ O₅ at least 0.5% but preferably below 5%

B₂ O₃ at least 0.5% but preferably below 5%

other elements 0 to 5%

all percentages being by weight of total composition and iron oxidesbeing measured as FeO.

The raw materials are placed in a furnace where they are heated to atemperature between 1,400° C. and 1,600° C. in order to produce a melt.In general, they are heated to at least 1,450° C., preferably between1,450° and 1,540° C., generally around 1,480° C. to 1,520° C.

The furnaces which can be used in the invention for forming the meltwhich is to be fiberised include cupola furnaces, oil and/or gas firedshaft or tank furnaces or electric furnaces. In these furnaces theinvention is particularly advantageous, although the composition alsoshows advantages when using other known types of furnace. Preferredfurnaces are those in which significant amounts of air are drawn. Slagformation and any volatilisation problems can be minimised by theinvention.

The melt is fiberised in any known manner. In particular it may befiberised by pouring into a fast-rotating cup having a substantiallyhorizontal base and perforated side walls out of which is thrown asfibres, or by pouring onto one or more spinning wheels. The or eachwheel is mounted on a separate horizontal axis. Melt poured onto thecircumference of the spinning wheel is flung off as fibres. Although asingle wheel can be used, preferably a cascade system is used in whichthe melt is poured onto the top rotor of a set of rotating rotors eachmounted about a different substantially horizontal axis and arrangedsuch that the melt is thrown from the top rotor onto the subsequentrotor, or on each subsequent rotor in sequence, in the set so as tothrow mineral fibres off the or each subsequent rotor into a collectionchamber. Any apparatus known for the fiberisation of mineral melts toform wool may be used but a particularly preferred apparatus isdescribed in our patent publication WO92/06047.

The fibres may then be collected as web or batt. The web may becross-lapped to form a batt. The batt may be consolidated into thedesired MMVF wool product in known manner.

Binder is usually included in the batt. For instance it may be sprayedinto the fibres before they are collected as a web or batt.

The wool may be in the form of shaped batts or other elements or it maybe in the form of tufts or granulates of mineral wool fibres, or in theform of articles made from such tufts or ganulates.

The MMVF wool may be used for any of the conventional purposes of MMVFwool, for instance as a horticultural growing medium, for sound or heatinsulation and protection, for fire resistance and protection and as afiller or reinforcement.

The following are examples of suitable compositions, (determined byX-ray fluorescence analysis and measured as weight %) and theirdissolution rate at pH 7.5 in nm per day. Each composition can be meltedin a cupola furnace and fiberised as in WO92/06047.

Compositions 1, 2, 3 and 4 are within the invention while 1A, 1B, 2A, 3Aand 4A are approximate comparisons and show that omitting the boronreduces dissolution rate. The comparative, borate free, compositionstend to slag formation, especially with the higher phosphorous contents.

    __________________________________________________________________________                                              Dissolution                         Compositions                                                                         SiO.sub.2                                                                        Al.sub.2 O.sub.3                                                                  TiO.sub.2                                                                         FeO                                                                              CaO                                                                              MgO                                                                              Na.sub.2 O                                                                        K.sub.2 O                                                                        B.sub.2 O.sub.3                                                                   P.sub.2 O.sub.5                                                                   Rate pH 7.5                         __________________________________________________________________________    1      53,4                                                                             3,6 0,5 2,5                                                                              16,9                                                                             10,1                                                                             3   0,5                                                                              5,1 3,2 65,5                                1A     56,4                                                                             3,5 0,5 1,8                                                                              19,7                                                                             10,7                                                                             4,3 0,5                                                                              0   2,8 40,3                                1B     54,6                                                                             4,3 0,6 2,8                                                                              15,6                                                                             10,6                                                                             4,7 0,6                                                                              0   1,3 8,6                                 2      58,1                                                                             3,3 0,5 2,1                                                                              18,9                                                                             10,3                                                                             3,4 0,5                                                                              3,2 2,5 53,9                                2A     56,4                                                                             3,5 0,5 1,8                                                                              19,7                                                                             10,7                                                                             4,3 0,5                                                                              0   2,8 40,3                                3      47,8                                                                             1   0,1 1,1                                                                              33,2                                                                             8,3                                                                              0,1 0,1                                                                              2,2 4   54,8                                3A     46,9                                                                             2,4 0,4 1,3                                                                              32 9,2                                                                              0,1 0,5                                                                              0   6   23,8                                4      54,2                                                                             2,4 0,1 3,9                                                                              21,2                                                                             8,2                                                                              0,1 0,3                                                                              5,9 2,2 57,9                                4A     53,2                                                                             3,2 0,1 7,3                                                                              23,4                                                                             5,3                                                                              0,1 0,3                                                                              0   3,6 16,7                                __________________________________________________________________________

We claim:
 1. Mineral wool formed of MMV fibres having a composition,expressed as oxides by weight of total composition, which comprisesSiO₂45 to 60% Al₂ O₃ 0.5 to 4% CaO 10 to 30% MgO 7 to 20% FeO 1 to 9% Na₂O+K20 0 to 6% Na₂ O 0 to 4% K₂ O 0 to 2% TiO₂ 0.1 to 2% and whichcomprises both P₂ O₅ and B₂ O₃.
 2. A wool according to claim 1 in whicheach of P₂ O₅ and B₂ O₃ is up to 10%.
 3. A wool according to claim 1 inwhich SiO₂ is 53.5 to 60% and FeO is 6.5 to 9%.
 4. A wool according toclaim 1 in which the composition comprisesSiO₂ 53.5 to 60% by weight CaO10 to 20% by weight MgO 10 to 20% by weight FeO 6.5 to 9% by weight P₂O₅ +B₂ O₃ up to 20%, by weight and each is up to 10%.
 5. A woolaccording to claim 1 in which the composition pomprises 7 to 15% MgO byweight.
 6. A wool according to claim 1 which comprises P₂ O₅ in anamount of 1 to 5% and B₂ O₃ in an amount of 1 to 10%.
 7. A woolaccording to claim 1 in which the amount of P₂ O₅ is 0.5 to 4.5% and/orthe amount of B₂ O₃ is 0.5 to 4.5%.
 8. A wool according to claim 1having a dissolution rate at pH 7.5 of at least 30 nm/day.
 9. A processof production of MMVF wool formed of MMV fibres having a composition,expressed as oxides by weight of total composition, which comprisesSiO₂45 to 60% Al₂ O₃ 0.5 to 4% CaO 10 to 30% MgO 7 to 20% FeO 1 to 9% Na₂O+K₂ O 0.1 to 2% P₂ O₅ +B₂ O₃ up to 20% and which includes both P₂ O₅and B₂ O₃ the process comprising providing raw materials to give thecomposition, providing a furnace, heating the raw materials in thefurnace to a temperature between 1,400° C. and 1,600° C. to provide amelt, fiberising the melt, and collecting the fibres as wool.
 10. Aprocess according to claim 9 in which the furnace is a cupola furnace.11. A wool according to claim 2 in which SiO₂ is 53.5 to 60% and FeO is6.5 to 9%.
 12. A wool according to claim 1 in which the amount of B₂ O₃is 1 to 5%.
 13. A wool according to claim 1 in which the amount of P₂ O₅is 0.5 to 5% and the amount of B₂ O₃ is 0.5 to
 5. 14. Mineral woolformed of MMV fibres having a composition, expressed as oxides by weightof total composition, which comprisesSio₂ 45 to 60% Al₂ O₃ 0.5 to 4% CaO10 to 30% MgO 7 to 20% FeO 6.5 to 9% Na₂ O+K₂ O 0 to 6% Na₂ O 0 to 4% K₂O 0 to 2% TiO₂ 0.1 to 2% P₂ O₅ +B₂ O₃ up to 20% and which includes bothP₂ O₅ and B₂ O₃.
 15. A process of production of MMVF wool formed of MKVfibres having a composition, expressed as oxides by weight of totalcomposition, which comprisesSiO₂ 45 to 60% Al₂ O₃ 0.5 to 4% CaO 10 to30% MgO 7 to 20% FeO 6.5 to 9% Na₂ O+K₂ O 0 to 6% Na₂ O 0 to 4% K₂ O 0to 2% TiO₂ 0.1 to 2% P₂ O₅ +B₂ O₃ up to 20% and which includes both P₂O₅ and B₂ O₃ the process comprising providing raw materials to give thecomposition, providing a furnace, heating the raw materials in thefurnace to a temperature between 1,400° C. and 1,600° C. to provide amelt, fiberising the melt, and collecting the fibres as wool.
 16. Aprocess according to claim 15 in which the furnace is a cupola furnace.